1. Field of the Invention
The present invention relates to an actual operating time indicator, more particularly, it relates to an actual operating time indicator for indicating an actual operating time of a hoist apparatus on a digital display. The present invention is advantageously used for an electric hoist apparatus which lifts a load up/down by using a motor, for example, a three-phase induction motor.
2. Description of the Related Art
A hoist apparatus for lifting a load up/down is widely used in various fields, for example, in a factory, a warehouse, construction and the like. There are mainly three types of hoist apparatus from a viewpoint of a motive power source, i.e., a compressed air type, an electric type, and a manual type. Although these types have individual advantages, the electric type is the most popular because this type has various merits from a viewpoint of cost/performance. The present invention relates to the electric hoist apparatus.
In general, an electric hoist apparatus has two motors, i.e., one is a lifting motor for lifting a load up/down, and the other is a travelling motor for moving the hoist apparatus in a traverse direction on a beam. The lifting motor is usually formed by a three-phase induction motor because of a simple/firm structure, relatively low cost and high power.
The lifting motor is defined by at least a rating load indicating a weight of a load in normal use, output power at the rating load, rating time for indicating a range of continuous use time, and a test load for indicating a maximum load.
In the above mentioned various fields, the hoist apparatus may be temporarily used in an overload state or over-time state. Accordingly, it is necessary to obtain precise data which can be utilized for maintenance of the apparatus after use for a certain time period. For example, it is necessary to precisely measure a relationship between a load and an operating time from a start point of use.
There are two main methods for indicating the actual operating time in a conventional art. That is, the actual operating time of the hoist apparatus is displayed by either an integrating wattmeter or a counter. However, the former merely indicates a so-called "total power-on time" for a certain period of time, and the latter merely indicates a number of times the hoist apparatus is operated.
Accordingly, in the above conventional art, the influence of a load during actual use of the hoist apparatus is not considered, for example, in an overload state or over-time state, so that it is impossible to precisely measure the actual operating time while taking the load into consideration.
Further, although the life span of a mechanism varies depending on the load during use, in the conventional art, the relationship between the life span of the mechanism and the load when measuring the actual operating time of the hoist apparatus is not considered. Accordingly, in the conventional art, the data are insufficient for maintenance so that it is impossible to efficiently maintain the hoist apparatus.